TOPIC: Renewing Free Ads

What would stop someone from continually renewing a free ad? Is there something in the program that keeps people logging in and setting up the same free ad several times instead of paying for a premium ad?

I didn't explain the question very well. If someone wants to cheat and not pay, he could enter a free ad, wait for it to expire, and enter a second free ad. Is there something in the program that stops someone from repeatedly entering free ads and cheating the system?